Heavy duty and other diesel engine types utilize a reductant in a diesel exhaust fluid such as urea in the treatment and reduction of NOx levels in the exhaust. The liquid urea is injected into the exhaust stream upstream of the SCR catalyst. However, when exhaust temperatures are low, the effectiveness of liquid urea in the treatment of NOx emissions suffers from drawbacks, such as the formation of urea deposits in the exhaust system. While superheating of the liquid urea can be used during low temperature conditions to obtain gaseous ammonia and reduce deposit formation, these systems are costly and impractical in many applications.
Solid storage media systems have been developed for ammonia storage in reductant delivery systems for selective catalytic reduction (SCR). The solid storage media systems typically provide a dry source of reductant, such as ammonia, stored in the solid storage media that is contained in a cartridge. The ammonia is released from the solid storage media in gaseous form as needed and delivered to an exhaust gas to treat emissions in an SCR aftertreatment system. However, these systems present drawbacks in heavy duty engine and other high volume applications due to the high cost of the cartridges and the need for frequent servicing to change the cartridge.
Therefore, there remains a need for further improvements in the architecture of reductant delivery systems, and in the control of reductant delivery systems to reduce NOx emissions in low temperature operating conditions, that are practical for heavy duty engine applications among others, while reducing cost and complexity. The present invention meets these and other needs according to the following described embodiments.